Jet propulsion motor



Aug 6, 1946. M. SUMMERFIELD 2,405,455

I JET PROPULSION MOTOR I Filed May 7, 1943 MARHN SUMMERFIELD IN VEN TOR.

.motor as a plurality of pairs of Patented Aug. 6, 1946 PATENT orrlcr.

JET PROPULSION MOTOR Martin Summerfield, Pasadena, Calif., assignor toAerojet Engineering Corporation, Azusa, Calif., a corporation ofDelaware 7 7 Application May 7, 1943, Serial No. 486,078

2 Claims.

This invention relates to jet propulsion and particularly to means andmethods for increasing combustion efficiency of jet propulsion motors.

A jet propulsion motor of the type to which my invention is particularlyapplicable comprises a tubular (substantially cylindrical) body havingan exhaust nozzle at one end and means for introducing liquidpropellants through injector orifices as separate streams into the otherend.

The space within the tubular memberbetween' a the injector and thenozzle throat serves as a combustion chamber. The propellant arespontaneously combustible.

The present invention contemplates the use of an injector at the end ofthe motor body 'opposite the nozzle and has particular reference to thearrangement of the motor parts and more particularly to the propellantfluid injector orifices and their arrangement with respect to thecombustion chamber. Jet propulsion motors constructed according to myinvention provided maximumcombustion efiiciency compatible with thenature of the propellants used and the mixture ratio required and henceprovide maximum thrust per unit weight compatible with theconditions ofoperation under which the motor is to be used which conditions may bespecified for exampl'e with respect to thrust, or operating time toreach a certaintemperature. I have found that the combustion efficiencyof such a motor can be made very nearly 100. percent, and that at oneend and the nozzle throat at the other end should be between about oneand three times .the inside diameter of the motor;

- 2. The combustion volume of the motor should be greater than 25 areaof throat (all units in inches) and preferably less than 200, when usinganiline and nitric acid at combustion pressures between 100 and 600 p.s. i. All of these conditions apply particularly to aniline and nitricacid. However, it is to be understood that I do not intened to belimited to the exact figures stated above and that for otherpropellants,

othernumerical values may be more suitable;

' 3. The propellantsshould be injected into the V streams havingindividual impingement points; 7 Y

7 4. Such impingement pointsshould be distributed substantiallyuniformly over the cross sectional area of the motor in front of theinjector;

5. The angle included between the propellant streams should be greaterthan about 30;

'5 6. The points of stream impingement should be spaced at least aboutaway from the wall of the injector;

7. The stream velocity should be at least 50 feet per second; 8. The twofluid propellants should be injected into the jet propulsion motor asseparate streams under such conditions that the streams 'of thepropellants will impinge and the momentum of. the resultant propellantmixture will be substantially parallel to the motor axis.

By'injecting propellants into the motor as a plurality of pairs ofstreams and distributing the points of impingement substantiallyuniformly throughout the cross sectional area of the combustion chamberthe initial flame area is distributed more uniformly over the motorarea. This gives an optimum distribution of propellants and henceincreases combustion eiiiciency. By injecting them at the end remotefrom the nozzle the components ofthe propellant mixture have anopportunity to burn for a long time as they flow under the influence ofcombustion energy from the injector end to the nozzle end;

These and other features of my invention may be more readily understoodby reference to the accompanying description taken in conjunction withthe drawing in which Fig. 1' is a cross sectional view of a jetpropulsionmotor incorporating my invention;

Fig. 1a is an end view of Fig. 1.

Fig. 1b is an elevation view of the orifice plate taken in section atline 1b-1b of Fig. 1;

Fig. 2 is a diagram showing a, distribution of impingement point overthe combustion chamber cross sectional area, which I have found to behighly satisfactory;

Figs. 3 and 4 are diagrams representing arrangements of eightimpingement'points, over 45 the same area; and

Fig. 5is a schematic diagram used in explaining my invention. p

In Fig. 1 I have shown a, jet propulsion motor having a tubularsection'l to one end of which 50 a nozzle 3 is secured by means of acollar 5 and a safety wire 1 connecting the collar to a safety wire lug9 welded. to the extension wall of the tubular section on the outsidethereof. At the other end of the tubular body there is secured 5'aninjector II by means of a collar I3.

Said injector comprises an orifice plate l and an injector back plateII. In the orifice plate there is a central recess forming a centralmanifold H which is connected by a first set of ports l9, l9" tocombustion chamber 2| in the interior of the motor. An annular recessforms a second manifold 23 which is connected to the combustion chamberthrough a second set of orifices 25', 25". The manifolds l1 and 23 maybe connected to corresponding liquid propellant supplies through thecorresponding elbow con nectors 21 and 29. A mounting ring 36'concentricwith and secured to the tubular section is provided for mounting themotor on an aircraft. t is desirable in the operation of jet pro pulsionmotors to supply propellants to the motor at predetermined rates and inpredetermined proportions. These rates may be desirable either tooperate the motor at maximum thrust or at a temperature suitable forgiving a sufficiently longer operating period to a motor of apredetermined thrust. The specific requirements depend on the use towhich the motor is to be put. Means may be accordingly provided 'forsup: plying a fuel through the ebow connector 21 into the centralmanifold I1 and thence to. the combustion chamber 2| through theorifices l9 and IS at predetermined rate and velocity. Means may also beprovided for supplying an oxidizing agentto the annular manifold 23through the elbow. connector 23 and thence to the combustion chamber 2|through orifices 25' and 25". Each pair of orifices |9, 25' and IS", 25"respectively direct the fuel and the oxidizer toward corresponding point3| and 3|" of impingement. A system for controlling the flow ofpropellants is described in detailin my copending patent applicationSerial No. 486,077; now abandoned. It can be shown that if the crosssectional areas of the orifices carrying oxidizer and fuel respectivelyare A1 and A2 respectively and thecorresponding densities and velocitiesof the propellants streaming 'therethrough are PiVi, andPzvzrespectively it can be shown 'that if the following relation holdsP1A1V12 sin a1=PzAzV2 sin a2 (1) where on and 4x2 are the angles thatthe're'spective streams form with the longitudinal axis X--X of themotor, then the resulting momentum of the propellant mixture afterimpingement will be parallel to the motor axis. Equation 1 means thatthe forces exerted by the two propellant streams impinging at eachimpingement point'3| and 3|" are equal and opposite."Expressed in stillanother way the transverse components of the momentum (that is thecomponents perpendicular to the motor axis) carried by the separatestreams per sec. to the respective points of impingement are equal andopposite. When the resultant momenum is substantially parallel to themotor axis, the propellant mixture, which is dispersed as a result ofthe collision of "the two streams, distributes itself substantiallyuniformly over the cross sectional area of the motor and very little ofit strikes the well there to condense and flow out the nozzle asunburned propellant. Because of this fact more of the propellants aresubjected to combustion under optimum combustion conditions, therebyresult ing in high combustion efiiciency.

In order to produce fine dispersion of the propellant mixtureby virtueof the, mutual impingement of the streams I utilize stream-yeloce itygreater than about 50' feet/second and cause 4 the streams to impinge ata large angle, preferably greater than about 30". However, the magnitudeof the impingement angle is limited by the fact that overheating of theinjector due to convection, conduction, and radiation of heat from theflame will occur, if the impingement points are closer than about 1 fromthe wall of the injector.

In order to further distribute the propellants over the cros sectionalarea of the motor I space the orifices on the injector in such a, waythat 7 the point of impingement will be substantially uniformly spacedover the cross sectional area of the motor. Thus for example in Fig. 2 Ihave shown diagrammatically how four impingement points 33 may bedistributed over the cross sectional' area of the combustion chamber.the outline of which is here represented by the circle 35. In thisarrangement the four impingement points are symmetrically spaced overthe cross sectional area'and at thecorners of a square having a diagonalapproximately equal to the radius ofthe' cross sectional area.Similararrangements may be readily applied when'any arbitrarily selectednumber of impingement points are utilized.

Figs. 3 and 4 show two possible arrangements of Simpingement points. InFig. 3 the impingement points 31 are closely spaced and at the center ofthe combustion chamber, and in Fig. 4 the impingement points 38 arespaced uniformly on a circle having its center on the axis of the crosssectional area and this circle has a radius about half that of the crosssectional area. While more uniform distribution of the propellantmixture could be obtained by spacing every other one of theseimpingement points closer to the wall of the motor chamber and theremaining impingement points closer to the center of the chamber I havefound it far simpler to space the impingement points uniformly on acircle as shown on Fig. 4 as this facilitates manufacture of theinjector. The arrangement area so as to. distribute them substantiallyuniformly throughout the cross sectional areaof the motor. 7 c

Equation 1 above only specifies a relationship between on, and 42 if thevalu sof 1, 2, Al, V1, and V2 are known.- The relationship betw n he v uis. termined by th mile f th pressu e r ps r s he Q ifice and he e-.quir d i ns f the re lentmixtu e- In order to reduce the amount of gaspressure e uired to drive he p o ll nt to he combustion chamber Iutilize orifices which are ro ndedhe ishr e ure de th r d u f theiro'unsection i blr be g etw about ne fourth and twice the diameter of therespective orifices. In this manner the drops in pre s e ous e r ficesej e ep smell and the loss; of pressure energyv supplied by the gaspressure drive means is kept small. This feature also assists inmaintaining a high combustion efficiency. By combining the variousprinciples hereinbefore set forth I am able to achieve high combustioneiflciency in jet propulsion motors.

I have observed that the efliciency of combustion is also afiected bythe relative directions of the momenta of the individual propellantmixtures formed at the various stream impingement points, and that thecombustion may be substantially completed in a shorter distance whenwhen the line of average momentum of such mixtures do not intersect eachother in the space between the injection points and the entrance to thenozzle. separate streams are preferably directed to points in the areaat the nozzle entrance on the same side of the motor axis as therespective impingement points. The maximum efficiency of combustion isobtained when these lines of momenta are substantially parallel to eachother, and to the motor axis, and the impingement points are distributedsubstantially evenly over the crosssectional area of the motor.

I claim:

1. In a jet propulsion motor comprising a tubular body section, anexhaust nozzle at one end of the tubular body and a propellant injectorat the other end of the tubular body, there being a longitudinal axisextending centrally through the body and centrally through the exhaustnozzle, said body, injector and exhaust nozzle forming a combustionchamber, the improvement which comprises a plurality of pairs ofpropellant injection orifices through the injector, means for supplyinga propellant fluid to one orifice of each pair, and means for supplyinga different propellant fluid to the other orifice of each pair, theorifices of each pair being directed so that their axes extend in thegeneral direction of said lorrgitudinal axis and intersect at a pointwithin the chamber, whereby the propellant fluids passing through theorifices of each pair impinge at said point, the positioning of saidorifices and the The momenta of the arrangement being such that theproduct of fluid density, stream cross-sectional area, the square ofstream velocity and the sine of the angle between the axis of the fluidstream and the longitudinal axis of the nozzle for one fluid streamequals that for the other stream whereby the direction of motion of thepropellant fluids after impingement is substantially parallel with saidlonigtudinal axis, the impingement points being substantially uniformlyspaced over the cross-sectional area of the combustion chamber.

2. In a jet propulsion motor comprising a tubular chamber having at oneend an exhaust nozzle and at the opposite end a fluid injection plate,means for introducing into the tubular chamber a plurality of propellantfluids, said means comprising a plurality of injection holes through theinjection plate and arranged in a circle symmetrically around thelongitudinal axis of the tube, and a second set of holes arranged in acircle of larger diameter than the firstmentioned circle, the axis ofeach hole of the first-mentioned circle being directed to meet the axisof an individual hole of the second-mentioned circle at a point ofimpingement within the chamber, said points of impingement being Iarranged in a circle within the chamber which has a diameterintermediate between that of the first-mentioned circle and that of thesecondmentioned circle, and means for supplying one propellant fluidthrough the first set of holes and another propellant fluid through thesecond set of holes, the arrangement being such that the product offluid density, stream cross-sectional area, the square of streamvelocity, and the sine of the angle between the axis of the fluid streamand the longitudinal axis of the nozzle for one propellant fluidsubstantially equals that of the other propellant fluid, whereby theresultant momentum of the propellant mixture after impingement issubstantially parallel to said longitudinal axis.

MARTIN SUMMERFIELD.

